1. Field of the Invention
The invention relates to a method and a device for detecting clogging in a fuel filter of a supply circuit of an internal combustion engine.
2. Description of the Related Art
The invention relates more specifically to the supply circuits of direct or indirect fuel injection engines, the supply circuits being of the type in which a fuel filter is arranged between a fuel pressure regulator, downstream of the filter and delivering fuel at an imposed pressure towards the engine, and a pump delivering fuel from a tank, this pump being disposed upstream of the filter and supplying the regulator via the filter, this pump generally being an electric pump, i.e. a pump driven by an electric motor.
Conventionally, these supply circuits, used with marine engines or motor vehicles and of the controlled ignition or compression ignition (diesel) type, are such that the pressure regulator, downstream of a supply rail of injectors, maintains a supply pressure of the injectors in this rail which is a substantially constant differential pressure between the fuel pressure and atmospheric pressure or the pressure at the air intake manifold to the engine, regardless of the fuel requirement of the engine, i.e. irrespective of the rate at which fuel is injected into the engine by the injectors, depending on the operating conditions of the engine, excess fuel being returned to the tank by the pressure regulator, as disclosed in particular by EP 0 577 477 and FIG. 1 of FR 2 725 244.
On diesel or controlled ignition high-pressure injection systems, the pump and regulator between which the filter is disposed are low-pressure components which do not supply the injector rail directly but supply a second, high-pressure pump and a second, high-pressure regulator which in turn supply the rail.
In other fuel circuits, the pressure regulator is upstream of the injector supply rail, between the inlet of this rail and the fuel filter downstream of the pump, and preferably close to the tank or inside it, on a bypass pipe opening into the tank, and the regulator is connected to the supply line between the filter and the rail intake, in which case the pressure regulator also returns excess fuel to the tank, as known from FIG. 2 of FR 2 725 244.
Other fuel supply circuits of the xe2x80x9cno return xe2x80x9d type are also known, i.e. without a passage for returning to the tank fuel in excess at the level of the pressure regulator, the latter also being omitted in certain circuits of this type where the electric supply of the pump is controlled by a sensor which detects the pressure prevailing in the supply line linking the pump to the injector supply rail so that the pump is electrically powered in order to impose a pressure at the pump output which is equal to the usage pressure required at the injectors.
In other circuits of the xe2x80x9cno return xe2x80x9d type, however, the fuel pressure regulator is a regulator-reducer supplying the injector supply rail and the power supply to the motor driving the pump is controlled by a pressure gauge disposed inside the tank or close to it and linked by a pressure tap to the supply line downstream or upstream of the filter between the pump and the regulator-reducer, so that the regulator-reducer is supplied with fuel at a pressure higher than the usage pressure required at the output of the regulator-reducer, as disclosed in U.S. Pat. No. 5,398,655 and FIGS. 4 and 5 of FR 2 725 244.
In the xe2x80x9cno return xe2x80x9d circuits known from the above-mentioned patents, the electric pump is controlled in a closed loop by measuring an operating parameter of the supply circuit, this being the fuel pressure at the pump outlet although it may also be the air delivery rate to the air intake manifold to the engine, which air flow rate is indirectly linked to the rate at which fuel is consumed by the engine, as disclosed in FR 2 686 947.
Furthermore, whether the fuel circuit does or does not have a return system for fuel in excess at the level of the pressure regulator, the circuit may be such that the pump is disposed in a fuel reserve dish, which is in turn arranged inside the fuel tank, and a part of the fuel delivered by the pump is diverted to this dish in the form of at least one fuel jet injected into the dish at a rate needed to prevent the pump from draining.
In all these known fuel supply circuits, in which the filter downstream of the delivery pump is often integrated with this pump in a sub-unit housed inside the fuel tank, it is evident that clogging in the filter may cause it to become blocked, at least partially, and disrupt smooth operation of the injection system of the internal combustion engine, or even interrupt its fuel supply. Because the filter is disposed inside the fuel tank and because the filter is not so readily accessible should it have to be replaced, it seemed desirable, not to say necessary, to provide some form of preventive or predictive maintenance for the filter in particular and to this end devise a method and a device for detecting clogging in this fuel filter.
To this end, the method proposed by the invention for detecting clogging in a fuel filter in a fuel supply circuit of an internal combustion engine, in which the filter is disposed on the one hand between a fuel pressure regulator downstream of the filter and of the type operating on a bypass system, delivering fuel at an imposed pressure upstream and towards the internal combustion engine, and, on the other hand, a pump for delivering fuel from a tank, the pump being disposed upstream of this filter and supplying the regulator across the filter, is characterised in that it comprises at least the following steps, which consist in:
determining the fuel pressure at the pump output and assimilating it with the fuel pressure at the intake of the filter,
determining the fuel pressure at the filter outlet as being the pressure imposed by the pressure regulator,
determining the drop in pressure of the filter on the basis of the difference between the intake and outlet pressures of the filter,
comparing at least one value based on said pressure drop with at least one reference value and deriving information therefrom relating to the clogging condition of the filter, preferably by determining that the filter is clogged if said value based on the pressure drop is higher than at least said reference value.
In order to determine the fuel pressure at the pump output or at the filter intake, this method may consist in measuring the fuel pressure by means of at least one pressure sensor between the pump output and the filter intake.
However, this involves using a pressure sensor which is an expensive component and in one particularly economical embodiment of the method proposed by the invention this method consists in determining the fuel pressure at the pump output on the basis of at least one relationship between said pump output pressure and at least one of the operating parameters of the pump, which are the instantaneous rotation speed of the pump, the mean supply current of an electric motor driving the pump and the thermal state of the pump.
In other words, the fuel pressure at the pump output may be determined by at least one operating model of the pump, taking account of at least the aforementioned operating parameters of the pump, and in particular the mean supply current of the electric motor driving the pump, since, in a known manner, this mean current enables the drive torque of the pump to be determined and this torque can in turn be used to determine the pump output pressure, in particular on the basis of characteristic curves.
In a simple manner, the method may include a step which consists in determining the mean supply current of the electric motor driving the pump by measuring a drop in voltage at the terminals of a shunt in the electric supply circuit of said motor.
However, a better quality operating model of the pump for the purpose of determining the pump output pressure in an open loop may be obtained if the instantaneous rotation speed of the pump and its thermal state are also taken into account.
Advantageously, to this end, the method may additionally consist in driving the pump by means of an electric motor with a commutating collector and determining the instantaneous rotation speed of the pump on the basis of at least the instantaneous rotation speed of the electric motor, which is determined by analysing the instantaneous current in the pump motor and detecting commutations of the collector of said pump motor.
In order to determine the thermal state of the pump, the method may additionally consist in simply measuring the temperature of the pump and/or estimating this temperature on the basis of at least one relationship between this temperature and at least one operating parameter of said pump, i.e. on the basis of a thermal model of the pump.
The step of comparing at least one value based on the pressure drop of the filter with at least one reference value may comprise at least one comparison of at least one absolute value of this filter pressure drop for at least one work rate or at least a given work rate range of the circuit with at least one threshold value for at least the same rate or at least the same fuel rate range and/or at least one comparison of at least one slope value of a variation of the filter pressure drop over time with at least one slope threshold for at least one work rate or at least a given work rate range of the circuit. Clearly, the threshold(s) for the absolute value and/or slope value of the variation of filter pressure drop over time is or are established and specifically indexed as a function of the rate in order to give sufficient advance warning before the filter is at risk of becoming substantially clogged, taking account of absolute or relative values measured or determined under the same rate conditions for other identical circuit filters and correlated with the state of clogging found in these filters on dismantling.
However, in order to improve the quality of preventive or predictive maintenance, it is of advantage to track changes over time in the pressure drop of a same filter and, to this end, the comparison step described above advantageously incorporates at least one comparison of at least one absolute value and/or slope value of the variation of filter pressure drop at a given instant with at least a similar value taken at at least one previous instant for at least one rate or at least a given work rate range of the circuit, and in particular at instants prior respectively to prior re-startings of the engine, the similar corresponding values being saved in memory when the engine is at a standstill.
Accordingly, the comparison steps in fact consist in comparing tables of measured and/or computed pressure drop values, specifically indexed on the basis of rate, with tables of reference values also specifically indexed on the basis of fuel rate.
In implementing the method outlined above, in order to detect clogging in a fuel filter disposed between the output of a pump driven by an electric motor and delivering fuel from a tank, and the intake of a fuel pressure regulator supplied by the pump via the filter and of the type operating on a bypass system which imposes a fuel pressure upstream and towards the engine, the invention also proposes a detection device which is characterised in that it comprises at least one electronic control unit, controlling operation of the pump and its electric drive motor, and which, on the one hand, knows the fuel pressure imposed by the regulator depending on the fuel requirements of the engine, and, on the other, determines the fuel pressure at the pump output on the basis of at least one operating parameter of the pump and/or the electric supply and/or operation of its electric drive motor, such as the instantaneous rotation speed of the pump, the mean supply current of the electric drive motor and the thermal state of the pump, said electronic control unit computing the pressure drop in the filter as being the difference between the fuel pressure levels at the pump outlet and imposed by the regulator, and comparing at least one value based on said pressure drop and/or at least one variation in said pressure drop with at least one reference value in order to deduce information about the state of clogging in the filter.